Two-part dental implant

ABSTRACT

A two-part dental implant includes distal and proximal stem portions which in an interconnected condition at least indirectly adjoin each other at a connecting location and have mutually facing surfaces in the region of the connecting location. A sealing body is provided between the mutually facing surfaces of the distal and proximal stem portions. The sealing body has sealing surfaces which face towards the mutually facing surfaces and which in the interconnected condition of the two stem portions bear sealingly against the mutually facing surfaces thereof. In addition, mutually facing abutment surfaces are provided between the distal and proximal stem portions. These mutually facing abutment surfaces bear against each other in the final assembled dental implant and limit the degree of approach of the two mutually facing surfaces of the stem portions between which the sealing body is arranged.

BACKGROUND OF THE INVENTION

1. Technical Field

The invention concerns a two-part dental implant. A distal implantportion is in the form of an artificial tooth root for implantation in ajawbone and a proximal implant portion carries an artificial toothcrown.

The invention concerns in particular the connection between the distaland the proximal implant portions, hereinafter also referred to as theimplant-abutment connection and abbreviated to IAC. The proximal end ofthe distal implant portion and the distal end of the proximal implantportion are of a geometrically mutually matching configuration andadjoin each other in the implanted condition of the stem.

2. Description of the Background Art

Dental implants serve to replace teeth which have been lost. Adistinction is drawn in relation to dental implants between one-part andtwo-part systems. The present invention concerns a two-part system.Two-part systems of that kind have a distal implant portion and aproximal implant portion. The distal implant portion is introduced intothe jawbone and there grows to the bone. The proximal implantportion—also referred to as the abutment—protrudes some millimetres intothe oral cavity and serves as an artificial tooth stump. In the presentcase the distal implant portion forms an artificial tooth root while theproximal implant portion forms the above-mentioned artificial toothstump. The proximal implant portion receives a tooth substitute of themost widely varying forms, for example in the form of a crown, andconnects it to the jaw by way of the distal implant portion.

The distal implant portion and the proximal implant portion are usuallyconnected together in the longitudinal direction by a screw pinextending in the longitudinal direction. The geometry of the connectingregion between the distal implant portion and the proximal implantportion is such that the connection between the two implant portions isof a force-locking nature or a positively locking nature or both.

The most important demands made on the connection between the distalimplant portion and the proximal implant portion are: the connectionmust be stable as it is subjected to enormous mastication forces. Thematching portions must be very precisely worked and may not have anygaps in the assembled state. The tooth structure is to be such that atany time it can be released from the implant and re-connected thereto.The tooth structure is to be such that it can also be replaced by othertooth structures. The two implant portions in the connected state mustbe rigid and without play and must be prevented from rotating about thelongitudinal axis of the implant. That is of particular significance ifa plurality of implants have been fitted in a jaw and those individualimplants are to receive a complex interconnected construction such asfor example a screwed fixed implant bridge. Such an implant constructioncan be appropriately accurately produced only when the implant portionsare exactly prevented from rotating. If a plurality of implantstructures are connected directly together, for example in the case of abridge substructure which generally carries a removable prosthesis, itis possible to dispense with a rotation-preventing configuration. Inregard to the demands already listed above, a further demand is made onthe bridge structures intended for that use: bridge structures mustafford the possibility that a plurality of interconnected toothstructures can then also be fitted on to the implants without anyproblem and connected thereto when the implant fixings, as usual, arenot introduced into the jaw in mutually parallel relationship.

Known two-part dental implants do not satisfy the above-indicateddemands to the desired degree. A particular problem in many knowntwo-part implants is the transition between the two implant portions.Known proposals for a solution in that respect, for example as disclosedin EP 0 842 643, U.S. Pat. No. 5,919,043, EP 1 371 342 or U.S. Pat. No.6,152,737, are not satisfactory.

SUMMARY OF THE INVENTION

The object of the invention is to provide a two-part dental implantwhich is improved in regard to the aforementioned demands.

According to the invention that object is attained by a two-part dentalimplant in which provided between the proximal implant portion and thedistal implant portion is a seal which is formed by means of a sealingbody and which seals off the oppositely disposed surfaces of theproximal and the distal implant portions in such a way that no germs andbacteria can enter.

Preferably the distal and the proximal implant portions have mutuallyfacing abutment surfaces which bear against each other when the toothimplant is in the final fitted condition. The mutually facing abutmentsurfaces limit the degree of approach of the two mutually facingsurfaces of the implant portions, between which the sealing body isarranged, and thus the maximum compression of the sealing body, insofaras the abutment surfaces define a minimum spacing of the two mutuallyfacing surfaces of the implant portions. That ensures that axial forcesacting on the implant such as mastication forces are not carried by thesealing body but are transmitted by way of the mutually facing abutmentsurfaces.

In a preferred variant of the sealing body those sealing surfacescomprise elastic material so that the sealing surfaces bear sealinglyagainst surfaces provided for that purpose on the distal and theproximal implant portion when the distal and the proximal implantportions are connected together. The seal and the proximal and thedistal implant portions are so designed that, after the definitiveconnection is made between the distal and the proximal implant portions,a surface pressure prevails between the sealing surfaces of the sealingbody and the corresponding surfaces of the two implant portions, whichis maintained even when the implant is subjected to mastication forcesand, as a consequence of such mastication forces, also suffers elasticdeformation in the region of the transition from the proximal to thedistal implant portion.

Accordingly, in accordance with the invention, provided between two endfaces which, in the case of a finally fitted, two-part stem, in thelongitudinal direction of the stem, are in mutually oppositerelationship and which are disposed outwardly in relation to the radialdirection of the stem, is a seal in the form of a sealing body which isof such dimensions that, upon axial loading on the dental implant, it isnot compressed in the axial direction of the stem and, in the event of alateral loading, always remains compressed by a minimum amount. Thus,when the implant is assembled, the seal is compressed only by thenecessary amount so that the implant-abutment connection ensures sealingintegrity under all possible circumstances. The degree of compression isdependent on the material and the thickness of the material, when usinga greater structural height for the seal, the compressibility of thematerial could turn out to be less in order to compensate for themovements in the region of the seal.

To fit the sealing body, there is preferably provided a sealing bodycarrier which serves as a positioning aid for the sealing body and whichcan already be fitted by the manufacturer of the sealing body so thatthe dentist who finally fits the implant in the finished condition caneasily fit the sealing body by means of the sealing body carrier.

The test described in greater detail hereinafter demonstrates that sealswith a sealing body of rigid material cannot ensure the desired sealingintegrity:

An implant being investigated was gripped rigidly in a holding device,to the level of the implant shoulder (proximal end of the distal implantportion).

The proximal implant portion was screwed on to the distal implantportion with a defined assembly force, by means of a screw pin.

A force of 100N at a 30° angle to the longitudinal axis of the implantwas applied to the proximal end face of the proximal implant portion andelastic (reversible) deformation of the material of the assembledimplant components was provoked thereby.

That gave the following measurement results:

The following variations occurred during the action of the force, in theregion of the two mutually facing surfaces of the two implant portions:

On the side where the force acted, the dimension of the nominaldimension intended for the seal (defined gap) increases by a value ≧1μm.

On the side opposite to where the force acted the magnitude of thenominal dimension intended for the seal (defined gap) decreased at thesame time by a value ≧50 μm.

The test was carried out with the materials of a titanium alloy(Ti6Al4V) and a ceramic (ZrO₂).

Those measurements supported the underlying realization of theinvention, that a rigid or plastically deformable seal does notrepresent any protection against the ingress of bacteria into thatregion.

Seals which are based on the principle of permanent deformation of asealing body function only in relation to connections, the components ofwhich are not subjected to the action of any forces.

Tooth implants serve to replace lost mastication members and thereforemust carry forces, referred to as mastication forces, and arepermanently subjected thereto. When using a rigid or ductile sealingbody, gaps which cannot be closed again are already produced when slightextra-axial forces and axial forces which exceed the assembly force ofthe screw connection occur. Accordingly, those connections cannot bereferred to as being bacteria-tight.

The forces required for the surface pressure between the sealing bodyand the respective implant portion can be produced in two differentways. On the one hand, during the step of connecting the proximal andthe distal implant portions, the sealing body can be elasticallycompressed between the two implant portions if the nature of theconnection—for example an axial screw connection—and the nature andarrangement of the seal are suitably selected. Here, an advantageousarrangement is one in which the sealing body is in the form of acircular disc with a central opening therethrough and is arrangedbetween two radially extending surfaces of the distal and the proximalimplant portions.

On the other hand, the seal can also have a sealing body which expandsafter the connection between the distal and the proximal implantportions is made. An arrangement of that kind can best be implemented ifthe surfaces of the two implant portions are in opposite relationship inthe radial direction so that an intermediate space to be filled by theseal between the proximal and the distal implant portions is to befilled by a sealing body which is in the form of a short tube whichpossibly narrows towards the distal end. It is advantageous if thesealing body has the elastic properties already described or is fittedinto the proximal or distal implant portion in its state of beingcontracted for example by cooling, then the respective other implantportion is connected to the first implant portion and the sealing bodyis then expanded, for example as a consequence of heating. The sameprinciple can also be applied to a seal in which the sealing body is inthe form of a circular disc with a central through opening.

Suitable materials for the sealing body are biocompatible plasticmaterials, in particular elastomers or duromers. That is also intendedto include a particularly suitable blend of rubber and PTFE. That blendpreferably contains carbon black as a filler. Thermoplastic elastomersand elastomer alloys (for example polypropylene from the group ofpolyolefins), thermoplastic materials (for example perfluoro elastomers(PTFE, FKM, FFKM, FFPM) and polyetheretherketone (PEEK) andthermosetting plastic materials (amino or phenoplasts) or a silicone canalso be considered as elastic plastic material for the sealing body.

Of those elastomers FFKM which contains PTFE as the base material isparticularly suitable as a filler silicic acid. Black coloration of suchan elastomer is to be achieved with carbon black and white coloration isto be achieved with titanium dioxide or barium sulphate. Silicic acidalone can already provide for adequate white coloration.

A sealing body which is also particularly suitable is one which isformed in large parts thereof by an elastomer which on its outside iscoated with a thermoplastic material or a duromer and more specificallypreferably with PTFE. In that case the elastomer permanently maintainsthe stress and the PTFE is mouth-resistant and provides for permanentsealing integrity.

Another suitable coating material is a dimer such as diapraxylylenewhich is also known as parylene and which can be applied to surfaces tobe coated, in a plasma coating process. Suitable layer thicknesses arebetween 0.5 μm and 50 μm. Layer thicknesses between 1 μm and 5 μm, forexample 3 μm, are particularly suitable. Structural formulae of such acoating material are shown hereinafter:

The surface of the parylene coating can additionally be provided with anano coating of metal such as titanium or silver—also in combinationwith a ceramic. The coating provides both for bacteria-tightness and atthe same time for neutral behavior in relation to cell tissue.

The respective surface to be coated is preferably polarized in order toincrease the adhesiveness thereof for the coating. Such a polarizationof the surface can be effected in a basically known fashion by means ofa plasma process.

In addition it may be advantageous for surfaces of the implant or itsconstituent parts, in particular the outwardly directed surface of thesealing body, to be polarized in order to achieve better bodycompatibility. Polarization provides that the adjoining tissue such asfor example bone and gums do not or cannot demonstrate rejectionbehavior in relation to the coating.

In regard to a possibly partially coated sealing body it is desirable ifthe coated surfaces do not have any sharp edges. Rather, all coatededges should be rounded in order to prevent the coating from flaking offupon deformation of the sealing body.

It is advantageous if the elastic material of the sealing body iselastically stretchable or compressible by at least 5%, better by morethan 20%. In an embodiment, by way of example, the spacing, which ispredetermined by the abutment surfaces, between the mutually facingsurfaces of the two-implant portions is 250 μm so that the seal involvesa nominal dimension of 250 μm. In this case the sealing body should bemade for example 50 μm over the nominal dimension (250 μm) of the sealso that after assembly a compression of 50 μm (20% compression) alreadyoccurs. Those values represent an ideal dimension that it is sought toachieve. The structural height of the seal should be as small aspossible in order for aesthetic reasons not to give away structuralheight for the later tooth crown; in particular dimensions between 0.1mm and 3 mm are considered as the nominal dimension. In terms ofdimensioning, it is crucial that the seal, even under the effect ofmastication forces, is deformed only in the range of elasticdeformability thereof and also always remains compressed by a minimumamount in partial regions, for example in the event of a lateralloading. Thus, when the implant is assembled, the sealing body iscompressed only by the necessary degree so that the implant-abutmentconnection ensures sealing integrity under all possible circumstances.The degree of compression is dependent on the material and the thicknessof the material, when using a greater structural height for the seal thecompressibility of the material can turn out to be less in order tocompensate for the movements in the sealing region.

For a sealing body which expands when heat is involved, in particularplastic materials with a high coefficient of thermal expansion of morethan 75×10⁻⁶/K at 20° are advantageous.

Preferably at least one outside surface of the sealing body, whichsurface forms the outside surface of the implant, is coated with a metalor ceramic layer in the manner described hereinbefore, in which case themetal-parylene or ceramic layer prevents bacteria from penetrating intoseal components which are covered by the metal or ceramic layer. A nanocoating, for example with titanium particles, is particularly suitable.The sealing surface itself can directly consist of a biocompatibleplastic material or can be coated in the above-mentioned manner. Inparticular titanium, silver or gold, optionally also in the form of aconstituent of an alloy, are considered as the material for the metallayer. All surface materials of the seals are mouth-resistant andsterilizable and do not absorb water or absorb-water only to a veryslight degree.

Besides elastic plastic material the sealing body may also include ametal spring or a separate plastic spring element of another plasticmaterial, such as for example PEEK. The spring element can be in theform for example of a plate spring or a ring of a u-shaped, inwardlyopen cross-section and ensures permanent elasticity and stressing forcefor the sealing body. A metal spring can be advantageous in particularin relation to a sealing body in which the elastic plastic material atleast partially comprises polytetrafluoroethylene (PTFE, Teflon),polypropylene (PP) or also polyetheretherketone (PEEK).

The invention is based on the realization that a two-part dental implantdoes not have any microgap in the region of the bone emergence point asit is precisely at that location that the implant-abutment connection(IAC) is to be found, that is to say the connection between the proximaland the distal implant portions. That connection causes a microgap, thatmicrogap in turn is the subject of scientific discussion at the presenttime. It is known that the bone resorbs to about 0.5 mm beneath theimplant-abutment connection (if it were exactly at the bone level). Itis demonstrated that the tissue adjacent the implant-abutment connection(gum and bone) shows signs of inflammation. It has been shown that thereare inter alia polymorphonuclear leucocytes which have priority inrelation to bacterially induced processes. The lack of sealing integrityof the IAC and the colonization thereof by bacteria is discussed as thereason for that phenomenon.

The result of bone loss is gingival recession with the consequence ofteeth becoming longer (implant crowns). Bone loss represents a majorproblem in aesthetically demanding regions such as for example in theregion of the front teeth.

The sealing body is preferably in the form of a ring which is to bearranged between two abutment surfaces extending perpendicularly to thelongitudinal axis of a respective implant portion, and provides forbacteria-tight sealing integrity. Such a sealing body or sealing ringpreferably comprises a plastic material which has greater elasticity orlesser hardness than the material of the two implant portions. The twoimplant portions preferably comprise a body-compatible metal, ceramic orplastic material.

In an advantageous variant of the two-part dental implant the mutuallyfacing surfaces of the two implant portions, between which the sealingbody is arranged, extend transversely with respect to the longitudinalaxis of the dental implant—that is to say in the radial direction—andparallel to each other. Such surfaces are particularly suitable forarranging between them a sealing body which is in the form of a circulardisc with a central opening therethrough. The central opening allows theconnection to be made between the proximal and the distal implantportions by means of a screw pin extending in the axial direction of theimplant. The screw pin also allows the sealing body to be sufficientlycompressed so that the desired surface pressure is produced between itssealing surfaces and the surfaces of the implant portions. The surfacepressure is limited in that case by the mutually touching abutmentsurfaces. In certain situations of use it is advantageous if the sealingbody is thicker in the region of its outer edges than in a centralregion of the seal. In that way the sealing body can be deformed in theregion of its edges upon assembly of the proximal and distal implantportions in such a way that its sealing surfaces bear exactly againstthe surfaces of the two implant portions. In alternative variants thesealing body however can also have sealing surfaces extending inparallel relationship with each other or it can be designed in themanner of an O-ring.

The geometry of the proximal and distal stem portion is preferably such,in the region of the transition between the two stem portions, that theconnection between the two stem portions is not only suitable fordirectly transmitting mastication forces from one stem portion to theother but at the same time is also non-rotational.

In accordance with a preferred embodiment a distal stem portion forminga distal implant portion has a longitudinal opening which is opentowards its proximal end and which has an inside wall having a geometryof a circular cross-section and into which are let V-shaped recesseswhich extend at least approximately in the longitudinal direction of thestem portion and which are open towards the proximal end thereof. Atooth structure stem portion forming a proximal implant portion has atits distal end an outside wall involving a basic geometry of circularcross-section, which fits into the longitudinal opening in the distalstem portion. Preferably the outside wall of the tooth structure stemportion, in the region of the distal end thereof, has v-shapedprojections which are matched to the v-shaped recesses in the distalstem portion in such a way that flank parts of the v-shaped recesses ofthe distal stem portion co-operate with flank parts of the v-shapedprojections of the tooth structure stem portion in such a way that thev-shaped projections of the tooth structure stem portion are pushed likea wedge into the v-shaped recesses of the distal stem portion until ineach case two flanks of a v-shaped projection and two flanks of av-shaped recess come into contact with each other and in that way fixthe relative position of the distal stem portion and the tooth structurestem portion without play both in the axial direction and also in therotational direction when the distal stem portion and the toothstructure stem portion are connected together or have been connectedtogether. The flanks which are in mutual contact act as abutmentsurfaces and form a defined heightwise abutment. The heightwise abutmentis represented by a defined geometrical form of the implant portionsthemselves. Thus the forces acting from above on the proximal implantportion (proximal stem portion) are transmitted only to the distalimplant portion (distal stem portion). If the forces acting were nottransmitted by way of the described heightwise abutment but by way of aseal that seal would be destroyed over the duration of the use.

In that respect the configuration of the distal stem portion affords theadvantage that it can also receive a tooth structure stem portionwithout v-shaped projections so that the mutually connected stemportions are as a result admittedly fixed relative to each other with avery high degree of accuracy in the axial direction, but not in therotational direction. That is advantageous in particular when the stemserves for fixing a bridge structure. Then no further element isnecessary for receiving the bridge structure. In the fitting operationthe person carrying out the treatment only has to screw a singleinterconnected element to the implant fixers which are in the mouth ofthe patient.

The flanks of the v-shaped projections or recesses respectivelypreferably extend radially outwardly in relation to a cross-sectionalplane extending transversely with respect to the longitudinal axis ofthe implant and thus extend perpendicularly to the peripheral direction.In that way, no radial forces which for example could burst a distalstem portion of ceramic are transmitted by way of the flanks which arein contact after fitting of the implant.

If the distal stem portion comprises a material of greater tensilestrength such as for example metal, in particular titanium, the flankscan also be inclined with respect to the above-described, strictlyradial orientation, in such a way that flanks belonging to a respectiveprojection of the tooth structure stem portion (that is to say theproximal implant portion) or a respective recess of the distal stemportion (distal implant portion) converge towards each other in anoutwardly directed direction. The flanks can be inclined for examplethrough 45° with respect to the radial direction and thus also withrespect to the peripheral direction. Accordingly the flanks have acentering action not only in relation to the rotational direction butalso in the lateral direction.

The basic geometry of the outside wall of the tooth structure stemportion is advantageously conical at least in the region of the v-shapedprojections. Correspondingly the basic geometry of the inside wall ofthe longitudinal opening of the distal stem portion is advantageouslyalso conical at least in the region of the v-shaped recesses.

For certain situations of use and in particular if the distal stemportion comprises ceramic it may be advantageous if the basic geometryof the outside wall of the tooth structure stem portion and also thebasic geometry of the inside wall of the longitudinal opening of thedistal stem portion are cylindrical at least in the region of thev-shaped recesses.

In both cases the fit between the outside wall of the tooth structurestem portion and the inside wall of the distal stem portion ispreferably a clearance fit at least in the region of the v-shapedrecesses.

In addition preferably provided on the distal stem portion and on thetooth structure stem portion are in each case four v-shaped recesses andv-shaped projections respectively, distributed uniformly over theperiphery of the respective stem portion. That affords four accuratelydefined positioning options in the rotational direction between thedistal stem portion and the tooth structure stem portion. Alternativelyit is also possible to provide more or fewer projections and recesses inmutually corresponding numbers, which are preferably equally distributedover the periphery of the respective stem portion. Suitable numbers arefor example 3, 6 or 8.

A projection of a widely opened V-shape (obtuse V-angle) in conjunctionwith a corresponding recess in the distal stem portion can also beappropriate.

Angles of between 10° and 170° are considered as the V-angles (angle ofspread of the respective V-shape). In the sense of a self-centeringdesign configuration, it is advantageous if in that case the V-angle isless than the tip angle of the respective friction cone which isafforded by virtue of the material pairing in the region of the mutuallyopposite flanks of the v-shaped projections and recesses respectively.

A separate aspect of the invention which can also be implemented in adifferent manner from that set forth in specific terms hereinbeforeprovides that, of those end faces of a distal stem portion and aproximal tooth structure stem portion which can encounter each otherwhen the two stem portions are assembled before the two stem portionshave assumed their definitive axial position relative to each other,none of the end faces is disposed in a plane extending perpendicularlyto the longitudinal axis of the two stem portions. In the case of knowntwo-part stems for tooth implants with means for preventing rotationalmovement, which generally have such end faces extending perpendicularlyto the longitudinal axis, which can butt against each other when stemportions are rotated relative to each other, before the two stemportions are completely pushed into each other in the desired fashion,there is the danger that a proximal tooth structure stem portion isfixed to a distal stem portion in a twisted position, with theconsequence that the stem produced by that incorrect assembly operationis of a greater length than is intended because the two stem portionsare not yet definitively pushed one into the other. The final fitsactually intended for defining the relative axial position of the twostem portions have not yet come into contact with each other in thatsituation because the twist as between the two stem portions relative toeach other means that initially at least one other surface extendingperpendicularly to the longitudinal axis of a respective stem portion isin a condition of bearing against an oppositely disposed surface of therespective other stem portion, which is actually not intended to comeinto engagement with the end face extending perpendicularly to thelongitudinal axis of the first stem portion. Automatic correction of therotational angle error also does not occur because the two surfaceswhich butt against each other in that way cannot slide against eachother in the manner of an inclined plane and in that way automaticallycorrect the rotational angle again.

In the case of known stems for tooth implants, a technician or aphysician carrying out the treatment must take care to precisely ensurethat the two stem portions are fitted one into each other without anyerror in terms of rotational angle so that the two stem portions are notfixed relative to each other in a wrong position.

In the case of the stem according to the invention that problem isavoided in that there are no end faces extending perpendicularly to thelongitudinal axis of the respective stem portion—apart from the surfacesintended for the purposes of definitive lengthwise end abutment. That isachieved in concrete terms by the v-shaped recesses and v-shapedprojections respectively. Other geometrical solutions however can alsobe envisaged.

That is based on the notion that the surfaces serving as thelongitudinal end abutment are arranged on a different radius from theother end faces which serve for positioning purposes in the rotationaldirection and which in the concrete case considered are formed by thev-shaped projections and recesses.

When the two stem portions are pushed one into the other the inclinedsurfaces of the oppositely disposed v-shaped recesses and v-shapedprojections respectively meet on an inclined plane. When the stemportions are further fitted together the flank surfaces which encountereach other slide one upon the other until the two stem portions haveassumed their axial relative end position with respect to each other andhave also adopted the correct rotational angle relative to each other.

Suitable materials for the distal and proximal implant portions are inparticular metals such as steel or titanium but also ceramic or plasticmaterial.

In order to provide implant portions which are true to shape in adesirable fashion the proximal and distal stem portions are preferablyproduced either by metal injection molding (MIM) or by hot extrusionmolding.

Metal injection molding makes it possible, in just one operating step,namely filling the injection molding mold, to impart to the entirecomponent its definitive geometry which can be of virtually anycomplexity.

Metal injection molding does not involve the use of a solid metal bodybut fine material as the starting material for the component to beproduced. That powder is mixed with a plastic material-bearing binderand kneaded to form what is referred to as a feedstock. The feedstock ispressed under high pressure at about 100° C. on a commercially availableinjection molding machine into an injection molding mold (tool) which isa negative representation of the respective stem portion. The greencomponent which is respectively produced in that way, for the proximalor distal stem portion, already involves the desired final geometry buthas to be freed of the binder again in the steps that now follow inorder to achieve a pure metal component. For that purpose, the binder isremoved in a multi-stage chemical and thermal process and at the sametime the component is ‘baked’ by way of a sintering operation at about1200° C. In that case the metal used is preferably titanium.

If the implant portions should not comprise metal but ceramic, ceramicinjection molding (CIM) is considered as a suitable production process.The CIM process functions precisely like the MIM process, the onlydifference lies in the use of the material. In this context alsoreference is made to feedstock with ceramic powder instead of metalpowder. Accordingly, ceramic constituents of the implant, in particularceramic stem portions, produced in accordance with an alternativevariant by CIM, are preferred.

Alternatively both stem portions can also be produced by cold or warm orhot extrusion molding.

For alternative manufacture of the proximal and the distal stem portionsby way of hot extrusion molding, two shaping tools have to be producedfor each implant geometry, for production of the connecting region ofthe implant-abutment connection.

The first shaping tool is produced for the process of hot extrusionmolding.

In the hot extrusion molding operation, the titanium is brought into therange of dynamic recrystallization (that means heated to a temperatureof between 700° C. and 900° C.).

The operation of shaping the tooth structure component (proximal stemportion) is referred to as warm solid forward extrusion molding or hotsolid forward extrusion molding.

The shaping operation for the implant portion (distal stem portion) isreferred to as warm cup backward extrusion molding or hot cup backwardextrusion molding.

For that purpose a round bar material is cut to length, heated andintroduced into the shaping tool. The shaping operation takes placeunder a high pressing pressure.

A first shaping step produces a result which already comes very close tothe final result which can be attained.

The overall geometry of the implant portions which form theimplant-abutment connection is already represented after the firstshaping step. There are still small tolerances present because ofthermal contraction of the cooled workpieces. In addition the surfacesare still dull by virtue of the severe heating of the workpiece, whichis necessary for the hot extrusion molding operation. When usingtitanium the risk of adhesion (the titanium sticking to the tool) doesnot arise.

In a further shaping step, the precise final form and smooth shinysurfaces in the region of the implant-abutment connection between thetwo stem portions are then achieved.

The second shaping step involves using a second shaping tool with whichcold calibration or warm calibration of the workpieces (proximal ordistal stem portion) is carried out.

The second shaping step can be effected at a point which is defined intime during the cooling phase after the first shaping step, at which theworkpiece is still at a temperature of between about 400° C. and 450° C.

For the second shaping step the respective workpiece is fullyautomatically removed from the first shaping tool and introduced intothe second shaping tool.

The variation in geometries due to the second shaping step is only veryslight as the preferred material titanium is very obdurate in itsbehavior in the cold and warm states in relation to a shaping procedure.After the metal lattice of titanium has begun to flow briefly andlocally, it becomes brittle quite quickly upon further shaping. Thetitanium structure is destroyed in the event of excessively substantialcold or warm shaping. With a very slight degree of shaping however,besides a defined final form for the workpieces in the region of theimplant-abutment connection, an increase in hardness is also achieved bylocal cold consolidation of the workpieces.

The shaping procedures are respectively terminated after the secondshaping step and the geometry described hereinbefore in relation to theimplant-abutment connection between two stem portions is finished.

The tool set required for the hot extrusion molding operation with thetwo above-described shaping steps, for shaping a respective implantcomponent, comprises in each case two shaping tools.

For production of the shaping tools, firstly graphite bodies areproduced on a 5-axis micromilling apparatus. To produce the shapingtool, the graphite bodies are eroded into a block of hardened steel bymeans of spark erosion.

The resulting surfaces of the shaping tool, which subsequently shape themass-produced parts, have to be polished by hand in a very laboriousprocess.

Possibly it may be necessary for one or both workpieces (proximal ordistal stem portion) to be further worked in regions outside theimplant-abutment connection.

The optionally required operation of shaping the workpieces to give thedesired final shape is achieved by cutting machining. That shapingoperation concerns the geometries of proximal regions of the proximalstem portion for corresponding tooth structures, for example crowns, aswell as the geometries of distal regions of the distal stem portion forproviding an artificial tooth root.

For a cutting machining shaping operation of that nature, the workpiecesmust be gripped in a workpiece holder of a suitable machine. For thatpurpose it is appropriate for the workpieces to be gripped at the exactgeometries of the workpieces, that are produced by the hot extrusionmolding operation, and held thereby during the cutting machiningprocess.

In order to exclude inaccuracies each workpiece is clamped only once forthe cutting machining operation.

A suitable machine for the cutting machining shaping procedure is aturning machining center, that is to say a machine on which allnecessary cutting machining steps can be carried out in succession.

To achieve the final shape for the tooth structure and the implant, ingeneral it is necessary to use both stationary tools (in the turningoperation) and also rotating tools (in the milling operation). An axialthrough bore in the proximal stem'portion and an axial bore with afemale screwthread for receiving a screw pin connecting the two stemportions is also formed by boring in that process.

BRIEF DESCRIPTION OF THE DRAWINGS

The Figures show in greater detail an embodiment by way of example of astem according to the invention for a dental implant including somevariants of the sealing body as well as an embodiment by way of exampleof a sealing body carrier as an auxiliary tool for assembly of the twostem portions. In the drawings:

FIG. 1 shows a perspective view of a tooth structure stem portion as aproximal implant portion,

FIG. 2 shows a perspective view of the distal stem portion as a distalimplant portion,

FIG. 3 shows a perspective view of the stem with interconnected distalstem portion and tooth structure stem portion, wherein the distal stemportion is shown in partially dotted line form,

FIG. 4 shows a perspective exploded view of the distal stem portion andthe tooth structure stem portion,

FIG. 5 shows a longitudinal section through the stem,

FIG. 6 shows a cross-section through the stem of the location indicatedby D-D in FIG. 5,

FIG. 7 shows an exploded view of the stem with all its constituent part,namely the proximal and distal stem portion, the sealing body and ascrew pin for connecting the stem portions to form the stem,

FIG. 8 shows a longitudinal section through the fully assembled stem ofFIG. 7,

FIG. 9 shows a longitudinal section through the distal stem portion,

FIG. 10 shows a further longitudinal section, turned through 30° withrespect to FIG. 8, through the distal stem portion,

FIG. 11 shows a longitudinal section through the proximal stem portion,

FIG. 12 shows a section similar to FIG. 8 but without the sealing body,

FIG. 13 shows a sectional view of a preferred configuration of thesurfaces, which are disposed outwardly with respect to the longitudinalaxis of the stem, of the distal stem portion and the proximal toothstructure stem portion and a sealing ring,

FIG. 14 shows a perspective outside view of the outside contour of apreferred transition from the proximal to the distal stem portion,

FIG. 15 shows a perspective detail view on an enlarged scale of avariant of a tooth structure stem portion in accordance with theembodiments of FIGS. 7 and 8,

FIG. 15 shows a detail view of a two-part dental implant with apreferred elastomer seal,

FIGS. 16 a to b shows the principle of the mutually facing abutmentsurfaces which limit maximum compression of the seal,

FIG. 17 shows a preferred annular sealing body of an elastomer,

FIG. 18 shows a detail view on an enlarged scale from FIG. 17,

FIG. 19 shows a sealing body as shown in FIGS. 17 and 18, partiallycoated with a nano coating,

FIG. 20 shows a sealing body similar to that of FIGS. 17 and 18 with aconcave outer peripheral surface,

FIG. 21 shows the sealing body 30 in its fully assembled, compressedcondition between the proximal and distal stem portions,

FIG. 22 shows a cross-sectional view of an alternative sealing body,

FIG. 23 shows the alternative sealing body of FIG. 22 in its fullyassembled, compressed condition between the proximal and distal stemportions,

FIG. 24 shows the alternative sealing body of FIG. 22 with a nanocoating,

FIG. 25 shows a view in cross-section of a second alternative sealingbody with nano coating and integrated metal spring,

FIG. 26 shows an enlarged portion of the second alternative sealing bodyof FIG. 25,

FIG. 27 shows the alternative sealing body of FIGS. 25 and 26 in itsfully assembled, compressed condition between the proximal and thedistal stem portions,

FIG. 28 shows the second alternative sealing body of FIGS. 25 and 26with a nano coating,

FIG. 29 shows an alternative variant of a seal,

FIG. 30 shows a perspective view of a sealing body carrier,

FIG. 31 shows an enlarged portion of the sealing body receiving means ofthe sealing body carrier in a perspective view as shown in FIG. 30,

FIG. 32 shows a longitudinal section through the sealing body carrier ofFIG. 30,

FIG. 33 shows an enlarged portion of the sealing body receiving means ofthe sealing body carrier in longitudinal section as shown in FIG. 32,

FIG. 34 shows a perspective view of the sealing body carrier withinserted sealing body,

FIG. 35 shows an enlarged portion from the perspective view of thesealing body carrier with inserted sealing body in FIG. 34,

FIG. 36 shows a longitudinal section through the sealing body carrierwith inserted sealing body as shown in FIG. 34,

FIG. 37 shows an enlarged portion from the longitudinal section of thesealing body carrier with inserted sealing body as in FIG. 36, and

FIG. 38 shows the sealing body carrier of FIGS. 30 to 37 with insertedsealing body when fitting the sealing body on to the proximal stemportion.

DETAILED DESCRIPTION OF THE INVENTION

In the two-part dental implant shown in the specific embodiments aproximal implant portion is formed by a tooth structure stem portion 10and a distal implant portion is formed by a distal stem portion 20.

As the perspective view of the tooth structure stem portion 10 shown inFIG. 1 illustrates, it has a longitudinal part 12 of a conical basicgeometry which narrows towards the distal end 14 of the tooth structurestem portion 10. The cone angle is 10°. In the region of that conicallongitudinal part 12 the tooth structure stem portion 10 has a total offour v-shaped projections 16 which face with their tips towards thedistal end 14 of the tooth structure stem portion 10. The four v-shapedprojections 16 act as triangular prongs and are symmetrical and arearranged at equal spacings from each other around the periphery of theconical longitudinal part 12 of the tooth structure stem portion 10.That affords eight flank surfaces 18 which face inclinedly towards thedistal end 14 of the tooth structure stem portion 10.

FIG. 2 is a perspective view showing the distal stem portion 20. It hasa longitudinal opening which is open towards its proximal end 22 andwhich has an inside wall 24 which is also of a conical basic geometry.Cut into the inside wall 24 are four v-shaped recesses 26 which haveflank surfaces 28 facing inclinedly towards the proximal end 22 of thedistal stem portion 20.

When the distal stem portion 20 and the proximal tooth structure stemportion 10 are connected together (see FIG. 3), the relative position ofthe two stem portions is very accurately defined both in the axialdirection and also in the rotational direction, by flank surfaces 18 and28 respectively which bear snugly against each other. The inclined flanksurfaces 18 and 28 respectively of the v-shaped projections and recessesrespectively thus form mutually facing abutment surfaces which limit theapproach of the two mutually facing surfaces 32 and 34 (see FIGS. 6 and7) and thus the maximum compression of the seal 30 (FIGS. 6 and 7). Thatis pictorially illustrated in FIGS. 12 a to 12 c. In particular FIG. 12c shows how the surfaces 18 and 20 are in contact and thus form alongitudinal abutment, in the final assembled condition of the dentalimplant.

Exact centering of the two stem portions is effected in the assemblyoperation by the respective mutually opposite inclined flank surfaces 18and 28 respectively of the v-shaped projections and recessesrespectively. Upon inserting the tooth structure stem portion 10 intothe longitudinal opening of the distal stem portion 20 the inclinedflank surfaces 18 and 28 of the projections and recesses respectivelymeet on an inclined plane. Thus upon further insertion into thelongitudinal opening of the distal stem portion 20 the tooth structurestem portion 10 slides until it reaches its axial final position and inthat situation rotates until all mutually opposite flank surfaces 18 and20 are in uniform contact with each other. As a result the toothstructure stem portion 10 is forced into its desired final positionwithout impediment to its sliding movement and can then be fixed by ascrew pin 40 extending in the longitudinal direction of the stem (seeFIG. 7). That screw pin 40 is tightened with a force of 30 Ncm.

The corresponding flank surfaces 18 and 28 which serve simultaneously asa longitudinal abutment and as a rotation-preventing securing means arethen advantageously sunk in the interior of the longitudinal opening ofthe distal stem portion 20 and are not disposed in the region of theimplant shoulder, as in other systems. The implant shoulder can thus beheld at exactly the same level.

In the variants shown in FIGS. 1 to 5 no particular measures are shownfor making the transition from the proximal tooth structure stem portionto the distal stem portion bacteria-tight in the region of the outsidecontour of the finished assembled stem.

In accordance with the variant shown in FIG. 6, provided for thatpurpose is a sealing ring 30 arranged between an outwardly disposed endface 32 of the proximal tooth structure stem portion 10′ and anoutwardly disposed end face 34, which is in opposite relationshipthereto, of the distal stem portion 20′. When the stem is in the finalassembled condition, that is to say when the proximal tooth structurestem portion 10′ and the distal stem portion 20′ have assumed theirdefinitive axial relative position with respect to each other, thesealing ring 30 is compressed in the axial direction. The sealing ring30 comprises a biocompatible plastic material.

FIG. 7 shows the essential component parts of the stem according to theinvention for a dental implant, as an exploded view, more specifically,the proximal stem portion 10, the distal stem portion 20, the sealingbody 30 for sealing off the transition between the proximal and distalstem portions and the screw pin 40 serving to screw the proximal anddistal portions together.

The longitudinal section through the stem according to the invention forthe dental implant in FIG. 8 has all of the essential component parts inthe final assembled condition, with a correspondingly compressed sealingbody 30.

FIGS. 9 to 11 show respective longitudinal sections of individualcomponent parts.

FIG. 12 shows how the flanks 26 and 28 of the projections 16 on theproximal stem portion 10 and the recesses 26 on the distal stem portion20 respectively co-operate in such a way that centering is effected byway of those flanks and not for example by way of the peripheralsurfaces, which are to be found therebetween, of the stem portions 10and 20.

The view of the transition between the tooth structure stem portion 10′and the distal stem portion 20′, which is a partly sectional perspectiveview on an enlarged scale in FIG. 13, shows that the outside contour ofthe fully assembled stem, in the transitional region from the toothstructure stem portion 10′ to the distal stem portion 20′, does not haveany gaps, in respect of which there is a risk of bacteria permanentlycollecting therein.

That can be seen equally from the outside view of the transition betweenthe tooth structure stem portion 10′ and the distal stem portion 20′ inFIG. 14.

FIG. 15 shows a perspective detail view on an enlarged scale of theproximal tooth structure stem portion 10′. The Figure shows a seat 36for the sealing body 30 as well as the v-shaped projections 16 whichhave already been discussed with reference to FIGS. 1 to 6.

FIGS. 16 a and 16 b shows how the flanks 18 and 28 act as abutmentsurfaces in the longitudinal direction and thus provide for definedcompression of the sealing body 30 (see also FIG. 12);

FIGS. 17 and 18 show a preferred sealing body 30′ comprising anelastomer such as FFKM, in cross-section. It will be seen that thesealing surfaces 36 of the sealing body 30′ are not flat but project inthe axial direction of the implant at the outer edge of the sealing bodyand in that way form ridges 42 and 44. Those ridges are deformed whenthe proximal and distal implant portions are tightly connected and thusproduce a secure sealing effect.

FIG. 19 shows the sealing body 30′ of FIGS. 17 and 18 with a coating 38of parylene, as is described hereinbefore. It can also be seen from FIG.18 that the coated edges of the sealing body 30′ are rounded in order toprevent the coating from flaking off in the region of those edges.

FIG. 20 shows that the outer peripheral surface 50 of the sealing bodycan be of a concave shape so that it is straightened to be asapproximately straight as possible as a consequence of compression ofthe sealing body after assembly of the stem according to the invention.

FIG. 21 shows the rounding of the edges of the sealing body 30 and thestem portions 10 and 20 at the locations marked by arrows.

FIGS. 22 to 24 show an alternative sealing body 30″ with an elastomerbody 60 in the form of an O-ring which is fitted into a ring element 62of inwardly open, u-shaped cross-section.

FIG. 22 shows a view in cross-section of the alternative sealing body30″. FIG. 23 is a view on an enlarged scale showing a part of thealternative sealing body 30″ in the fitted condition between theproximal stem portion 10 and the distal stem portion 20. FIG. 24 showsthat the alternative sealing body 30″ can also have a coating 38 forexample of parylene.

FIGS. 25 to 27 show by way of example a further alternative variant of asealing body 30′″ which has a metal spring 48 in its interior. The metalspring 48 is disposed in an elastic plastic material body 46 which is ofan annular configuration and which is of a u-shaped, inwardly opencross-section. The plastic material body preferably comprises PTFE andthe metal spring 48 comprises stainless steel. As FIG. 26 shows theplastic material body 46 can have a coating 38, for example of parylene,on its outside. On its outside, the plastic material body 46 is coveredwith a layer 38 which is a few nanometers thick and which in theillustrated preferred variant contains titanium particles. The thicknessof the layer 38 is shown in greatly exaggerated form in the Figure inorder to make the layer visible. A nano coating of that kind can beprovided on all outside surfaces of the sealing body, more specifically,irrespective of the external form of the sealing body.

In alternative variants the springs can also comprise another resilientmaterial, for example titanium or a plastic material such as PEEK. Thesprings can also be of a different form as long as they exert a springaction in the longitudinal direction of the sealing body, as indicatedby the dash-dotted line (see FIG. 25).

FIG. 28 shows a sealing body in which an annular plastic material body28′, for example of PTFE, of inwardly open, u-shaped cross-section, ispartially filled with elastomer 64.

FIG. 29 shows a seal having a sealing body 30″″ comprising an expandablematerial such as for example expandable metal or a plastic material witha high coefficient of thermal expansion. The sealing body 30″″ of FIG.29 is in the form of a tube portion. The intermediate space between theproximal and the distal implant portions 10″″ and 20″″ respectively isof a corresponding configuration.

FIGS. 30 to 38 show a sealing body carrier 70 which serves as a tool forfitting a sealing body 30 on the proximal stem portion 10. At one endthe sealing body carrier 70 has an inwardly open groove 72, into which asealing body 30 can be inserted. Preferably the sealing body carrier 70is fitted with the sealing body directly after manufacture of thesealing body 30 by the manufacturer thereof. That facilitates handlingby the physician and improves hygiene. An externally fluted grippingregion 74 facilitates handling in that respect.

1-29. (canceled)
 30. A dental implant comprising: a two part stem havinga separate distal stem portion adapted for implantation in a jawbone anda separate proximal stem portion adapted to receive an artificial toothstructure, the distal stem portion having a longitudinal opening whichis open towards the proximal end of the distal stem portion and has aninside wall having a basic geometry of circular cross-section, theinside wall defines V-shaped recesses which are open towards theproximal end of the distal stem portion, the proximal stem portion atits distal end having an outside wall with a basic geometry of circularcross-section which fits into the longitudinal opening of the distalstem portion, the distal and proximal stem portions in an interconnectedcondition at least indirectly adjoin each other at a connecting locationand have mutually facing surfaces in the connecting location, themutually facing surfaces extend transversely with respect to alongitudinal axis of the dental implant, the distal and proximal stemportions have mutually facing abutment surfaces which bear against eachother in the interconnected condition and which limit the degree ofapproach of the two mutually facing surfaces of the stem portions sothat the abutment surfaces define a minimum spacing of the two mutuallyfacing surfaces of the stem portions; and a sealing body providedbetween the mutually facing surfaces of the distal and proximal stemportions at the connecting location, the sealing body having sealingsurfaces which face towards the mutually facing surfaces and which inthe interconnected condition of the two distal and proximal stemportions bear sealingly against the mutually facing surfaces thereof,the sealing body bridges over the minimum spacing of the two mutuallyfacing surfaces of the stem portions.
 31. A dental implant according toclaim 30, wherein the mutually facing surfaces are of a conical shape,are of the same cone angle and are arranged concentrically relative toeach other and relative to a longitudinal axis of the dental implant.32. A dental implant according to claim 30, wherein the sealing body isin the form of a circular disc with a central opening therethrough. 33.A dental implant according to claim 30, wherein the sealing body hasconcavely shaped end faces so that the material thickness of the sealingbody, measured in the longitudinal direction of the implant, is greaterat least in the relaxed condition in the region of the peripheral edgeof the sealing body than in a central region of the sealing body.
 34. Adental implant according to claim 30, wherein the sealing body is atleast partially comprised of an elastic material.
 35. A dental implantaccording to claim 34, wherein the elastic material of the sealing bodyis elastically compressible by at least 5% of a direction in which itextends.
 36. A dental implant according to claim 34, wherein the elasticmaterial of the sealing body is a plastic material.
 37. A dental implantaccording to claim 36, wherein the plastic material is an elastomer, athermoplastic material or a duromer blend.
 38. A dental implantaccording to claim 36, wherein, besides plastic material, the sealingbody has at least one metal or ceramic constituent.
 39. A dental implantaccording to claim 37, wherein the plastic material has a coefficient ofthermal expansion of more than 75×10⁻⁶/K at 20° C.
 40. A dental implantaccording to claim 30, wherein at least one outside surface of thesealing body, that forms an outside surface of the implant, is coatedwith a metal, ceramic or plastic layer, wherein the metal, ceramic orplastic layer prevents ingress of bacteria into constituent parts of thesealing body which are covered by the metal, ceramic or plastic layer.41. A dental implant according to claim 40, wherein the metal layercontains titanium, silver and/or gold or the plastic layer containsPTFE.
 42. A dental implant according to claim 30, wherein at least thesealing surfaces of the sealing body comprise an elastic, biocompatible,mouth-resistant, sterilizable plastic material.
 43. A dental implantaccording to claim 30, wherein the sealing body is arranged in a radialfree space between the mutually facing surfaces of the distal andproximal stem portions, wherein the extent of the sealing body in aradial direction is greater than the free space between the distal andthe proximal stem portions in the completely interconnected conditionthereof.
 44. A dental implant according to claim 30, wherein the outsidewall of the proximal stem portion in the region of the distal endthereof has V-shaped projections which are matched to the V-shapedrecesses of the distal stem portion in such a way that when the distalstem portion and the proximal stem portion are connected together, theV-shaped recesses and the V-shaped projections cooperate in mutualcontact and form the mutually facing abutment surfaces.
 45. A dentalimplant according to claim 44, wherein the distal stem portion has fourof the V-shaped recesses which are distributed uniformly over theperiphery of the inside wall and the proximal stem portioncorrespondingly has four of the V-shaped projections which are alsodistributed uniformly over the periphery of the outside wall.
 46. Adental implant according to claim 44, wherein the outside wall of theproximal stem portion which is generally conical in the region of theV-shaped projections.
 47. A dental implant according to claim 48,wherein the outside wall of the longitudinal opening of the distal stemportion has a basic geometry which is conical in the region of theV-shaped recesses.
 48. A dental implant according to claim 30, whereinthe sealing body is of such dimensions that it is compressed in an axialdirection of the stem when the distal stem portion and the proximaltooth structure stem portion have assumed their definitive axialrelative position with respect to each other.
 49. A dental implantaccording to claim 48, wherein the sealing body is a circular sealingring of rectangular material cross-section.
 50. A dental implantaccording to claim 48, wherein the sealing body is made from abiocompatible plastic material.
 51. A dental implant according to claim30, wherein at least one of the distal stem portion and the proximaltooth structure stem portion is made from biocompatible material.
 52. Adental implant according to claim 51, wherein the biocompatible materialis titanium or a titanium-bearing alloy.
 53. A dental implant accordingto claim 30, wherein at least one of the distal stem portion and theproximal stem portion is made from ceramic.
 54. A dental implantaccording to claim 53, wherein the ceramic contains ZrO₂,ZrO₂/Al₂O₃/Y₂O₃ (ATZ), ZrO₂/Y₂O (TZP) or ZrO₂/Y₂O₃/Al₂O₃ (TZP-A).
 55. Adental implant according to claim 30, wherein at least one of the distalstem portion and the proximal stem portion is made from plasticmaterial.
 56. A dental implant according to claim 30, wherein thesealing body has an outer peripheral surface which forms an outersurface of the two part dental implant when assembled.
 57. A dentalimplant according to claim 30, wherein, the mutually facing surfacesextend parallel to each other.